SITE INFORMATION AND CORRESPONDENCE_FILE 2

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ENVIRONMENTAL HEALTH DEPARTMENT i " SAN JOAQUIN COUNTY yDonna K. Heran, R.E.H.S. unil Supervisors < Director 304 East Weber Avenue, Third Floor Cal sorgman, R.E.H.S. Laurie A. Cotulla, R.E.H.S. Stockton., California 95202-2708 Mike Huggins, R.E.H.S. , R.D.I. Program Manage Telephone: 209 468-3420 Douglas W. Wilson, R.E. H.S , p ( ) Margaret Lagorio, R.E.H.S. Fax: (209) 464-0138 Robert McClellan, R.E.H.S. Website: www.sjgov.org/ehcf/ Leff Carruesco, R.E.H.S. RAYMOND FARMER BESS FARMER 3810 FOURTEEN - MILE DR FEB 117 20M STOCKTON CA 95219 RE: TOYOTA TOWN SITE CODE: 1151 610 HUNTER ST STOCKTON CA 95202 During a telephone conversation between San Joaquin County Environmental Health Department (EHD) and your consultant, ATC & Associates (ATC), on February 6, 2006, ATC proposed replacing the current soil catalytic treatment unit of the vapor extraction (SVE)/air sparging (AS) system with a more cost-effective treatment system, specifically, granulated activated carbon (GAC) due to decreasing contaminant concentrationSin the vapor samples. With the exception of several intermittent shut-down periods, the SVE system has been in operation since December 2002. EHD has reviewed the 3'dQuarter 2005 GroundivaterMonitoring Dort QMR) dated January 18, 2006, prepared by ATC, the contaminant concentration of the influent vapor samples has decreased from a high of 3,500 parts per million by volume (ppmv) of Total Petroleum Hydrocarbons as gasoline (TPH-g) and 9.2 ppmv of benzene in January 2003, to 39 ppmv in October 2005, and 6.4 ppmv of TPH-g and 0.073 ppmv of benzene in January 2006 (the 2006 results were submitted to EHD via email by ATC). ATC calculated 56.41 pounds of TPH-g were removed by the SVE system in 1 ,436.5 hours operation during the third quarter 2005, using an average concentration of 57 ppmv of TPH-g. _ In comparison, ATC had originally calculated a removed mass of 1,270 pounds of TPH-g in 1,587 hours of operation at 778 ppmv of TPH-g for the second quarter of 2003. The quarterly mass removed had dropped to 57 pounds of TPH-g in 1,355 hours of operation at 44 ppmv of TPH-g by second quarter of 2004 (2xd Quarter Report 2004) . The contaminant concentration in the influent vapor had decreased significantly and leveled out by 2004. EHD concurs with ATC's conclusion that there is enough soil vapor mass still being removed from the vadose zone and volatilized mass being stripped from groundwater to warrant the continued operation of the SVE/AS system. Since the contaminant removal rate is relatively low, treatment of influent vapor before discharge may not be necessary. Please contact San Joaquin Valley Air Pollution Control District on emission regulations, and submit the most cost-effective work plan or proposal, to either replace or remove the vapor treatment unit to EHD by March 15, 2006.